How does `ReversedCollection.reverse` typecheck?

[xwu (Xiaodi Wu)]

@Ben_Cohen

I'm not sure what you mean by conditional extension, I don't think either of these methods are from conditional conformances. ReversedCollection requires its base be bidirectional, but we don't normally describe that as conditional.

I don't know enough about symbol graph to say if your question 2 is behaving as expected.

As per my caveat, the observation was based on reading @taylorswift's documentation website, which uses language stating that the conformance to BidirectionalCollection exists only when Base conforms also: that would be redundant since Base always conforms, but also not impossible to spell (extension ReversedCollection: BidirectionalCollection where Base: BidirectionalCollection).

Checking the original source, ReversedCollection indeed conforms unconditionally to BidirectionalCollection (which is what I'd have guessed to begin with), so this can't explain the symbol graph issue.